(a) Field of the Invention
The present invention relates to a bearing that is mounted on a rotary shaft of a rotator and supports the rotary shaft perpendicular to or in parallel with (axially) the rotary shaft.
(b) Description of the Related Art
In parts (a rotary shaft and a moving shaft) that make motions such as rotation or reciprocation, various types of bearings are provided to solve problems such as wear or damage of the parts, noise, and waste of energy due to friction that may be generated in the motions of the parts. The bearing on which loads are applied perpendicular to the rotational axis is called a radial bearing or a journal bearing (for sliding bearings), and the bearing on which loads are applied in parallel with the rotational axis (that is, axially) is called a thrust bearing. Most bearings are thrust bearing, and roller bearings are classified as thrust bearings when axial loads are applied over 45 degrees and as radial bearings in remaining cases.
A thrust bearing is mounted on rotary shafts because axial vibration is generated in a rotator that rotates at a high speed. In general, for devices including various rotary shafts, such as power generators or turbines, thrust bearings for reducing axial vibration are generally used with radial bearings for reducing radial vibration. Particularly, the rotators that rotate at high speeds need to be used at high temperature and to be able reduce noise because friction necessarily increases temperature. Further, the rotators require high durability to prevent bearings from being damaged due to axial loads. Because of those conditions, fluid bearings have been generally used as thrust bearings or bearings that are at least supplied with fluid that is a lubricant have been widely used.
Further, recently, a divisional type of power generation technology has been more commercialized all over the world due to an increase in costs for initial installations because the cost per kilowatt for transmitting power is high in centralized systems, and there is a need for inexpensive basic structures to distribute generated power to consumers. With this tendency, gas microturbines that are small gas turbines capable of generating power at specific sites are being increasingly used. Gas microturbines generally have an output of less then 1 kW or of hundreds of kilowatts. Those gas microturbines are being increasingly developed and used for divisional power generation and small-scale cogeneration systems because of technical advantages and environmental friendliness.
It has been known that the rotary shafts of small devices such as the gas microturbines usually rotate at high speeds of 10,000˜400,000 rpm in order to achieve desired output. Radial bearings and thrust bearings are necessary for such small devices. In particular, for small high-speed rotators such as gas microturbines of which the necessity for and the actual use of are increasing, there is an increasing need for bearings that can be reduced in size and weight while satisfying the conditions of a non-contact type and no oil supply, in addition to the conditions required for bearings, that is, reduction of axial vibration, usability in high-temperature environments, and high durability.
In general, the bearing systems of rotators are composed of a radial bearing that supports radial loads and a thrust bearing that support axial loads, as described above. However, there is a problem in that the bearing systems on rotators necessarily increase in volume, because the bearings are separate parts. The larger the volume of the bearing systems, the larger the length of rotators becomes, and accordingly, the primary bending mode (critical speed) of the rotators is lowered, which causes a problem in that the stability of small rotators is considerably decreased during high-speed rotation.
Further, in the process of separately manufacturing the two types of bearings and assembling them, a specific back plate for mounting the thrust bearing is needed and there is a need of a process for fitting the degree of precision in assembling, thereby causing the assembly process to be complicated. In addition, as described above, in order to satisfy the conditions of non-contact type and no oil supply, it is difficult to use ball bearings and sliding bearings, which are widely used, and it is required to use air foil bearings and electromagnet bearings, but those bearings have the following problems. The air foil bearings are practically difficult to use, particularly for a thrust bearing, due to very poor structural durability, and there is a limit in reducing the size of a bump foil. The electromagnetic bearings have a problem in that the configuration of the devices is complicated and expensive, so they are not economical.
Further, the following problems have been generated with the progress of studies for improving the shapes of small rotators such as those used in the gas microturbines described above. FIGS. 8A and 8B are views showing the arrangement of bearings on a rotary shaft coupled with impellers in the related art. In the related art, a turbine impeller 2 and a compressor impeller 3 are separately fitted on a rotary shaft 1. That is, the impellers 2 and 3 are fitted at an end portion of the rotary shaft 1 and then fixed by thread fasteners. In order to combine the rotary shaft-impeller assembly and a bearing 10 that is generally used in the related art, the bearing 10 is also fitted when the impellers 2 and 3 are fitted onto the rotary shaft 1.
However, in the rotator having this configuration, imbalance and bending between the rotary shaft rotating at a high speed and the parts on the end of the rotary shaft are problematic. As a way of solving the imbalance and bending during high-speed rotation, a technology of manufacturing a rotary shaft and impellers as one unit, breaking from the way of separately manufacturing a rotary shaft, a compressor impeller, and a turbine impeller and then assembling them, has been studied in recent years. However, with design and development of a rotator configured by integrating a rotary shaft and impellers due to the problem of imbalance that is generated when a rotary shaft and impellers are combined, there is another problem in that it is very difficult to combine the bearings of the related art with the integrated impellers and rotary shaft.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.